My Hornby A3 "Flying Scotsman" in NRM LNER format (bought around 2013) has always suffered from a lot of wheel slip when pulling a rake of 6 coaches in a 600 mm radius curve.
For information, my Hornby A4 "Great Snipe" does not exhibit the same wheel slip problem with the same or other rakes of 6 coaches.
The A3 has also been a bit jerky under DCC control when operating at slower speeds - less than speed step 10.
Note that a set my decoders using the speed table such that the scale speed (mph) = speed-step / 2 for express passenger locos and = speed-step / 3 for other locos
Early September 2019 I noted that the A3 was also now very noisy (scraping sounds) and even more jerky even at higher speeds.
Cleaning the wheels and some light lubrication to axles, connecting rods and even the motor bearings and gears did not solve the noise and jerkiness.
Eventually I removed the intermediate gear and ran the motor alone and found it was noisy (scraping noises) at higher speeds.
I decided on a bit of research before buying a replacement Hornby X4026 direct replacement 5-pole motor (refer Hornby Service Sheet HSS 388).
Having previously (March 2019) replaced the 3-pole motors in two Hornby D16/3 locos with motors intended for the Hornby K1 that were 5-pole plus flywheel resulting in far better slow speed running I looked for an alternative to the X4026.
From photos the motor (part X6711) for the Hornby Crosti 9F (loco R3273) appeared to be the same plus a flywheel at the non-gear end. Hornby and many websites were silent on whether this was a 5-pole motor however a couple of Hornby retain outlets did mention 5-pole in the description for the Hornby Crosti 9F.
I took a chance and ordered a Hornby X6711 from Peters Spares in the UK which duly arrived a week ago. I also as a precaution ordered a spare set of the original A3 motor retaining parts in case my change-out idea proved unsuccessful. Comparing the X4026 and the X6711 motors externally they were the same dimensions. Using a torch and counting the pole segments found both were the same - that is 5-pole.
This weekend I removed the original X4026 motor from the Hornby A3, modified (cut a slot in) the rear motor retaining so as to allow it to slide over the motor shaft between the motor housing and the flywheel.
The X4026 also have two parallel faces on the sides of the part where the rear of the motor body sides into the rear retainer bracket whereas the X6711 is circular so a judicial easing of the retaining bracket for a good fit.
Then it all went together beautifully. A test run and there was no further sounds and there was no jerkiness at slow speeds.
I also undertook a further minor modification while I had the A3 apart to try and improve the traction and prevent wheel slip when pulling a rake of 6 coaches.
The A3 chassis has a location on top between the front and centre drivers where a decoder could be installed - albeit that the actual 8-pin decoder socket was installed in the tender.
I removed the two stubs intended to hold the decoder socket and in that space placed some steel strips that totalled 20 grams. This combined with 10 grams increase for the flywheel (behind the rear drivers) resulted in a total increase of 30 grams weight.
This has proved to be sufficient to:
(a) prevent wheel slip when pulling a rake of 6 coaches in a 600 mm radius curve, but
(b) if one holds the tender stationary the loco wheels will still slip so that in operation an unforeseen event causing the loco to physically stop cannot stall the motor and potentially lead to a burn-out of the motor windings.
Various threads on various websites are mixed on the topic of adding extra weight to locomotives.
Some folks claim it should not be done - primarily because it could overload the motor and cause a motor winding failure (overheating)
Others propose quite significant additions in weight - suggesting they add weight even around 150 grams in some cases.
Some do rightly highlight the need to keep or improve the loco balance with the added weight over the driving wheels - extra weight in the smokebox can be detrimental and reduce the traction of the rear wheels.
I understand that the DCC Concepts "PowerBase" is in fact steel segments placed under the track with a magnet attached to the loco to increase adhesion of the wheels - akin to the old (1960's era) Hornby "Magnahesion"
The conclusion from my perspective is that:
(a) changing out the Hornby X4026 motor to an X6711 (5-pole with flywheel) results in smoother slow speed operation, and
(b) a little extra weight (say 30 grams = ~ 1.1ounce) helps prevent wheel slip pulling a rake of 6-coaches in a 600 mm radius curve.
I have attached a number of photos here to show what I have done.
The Hornby A1 and A4 series also apparently from the respective Service Sheets use the X4026 motors and thus tentatively, subject to space behind the motor, the same motor change-out could be undertaken.
